How to charge a small (50ah) lifepo4 battery on a lead acid powered boat?

[diogocyrineu]

So, I have a 32 feet monohull boat and live in it.
We have 500w of solar with MPPT for it and house bank of 315ah of lead acid and an 105ah lead acid for the motor with an alternator that can charge both banks.
I have a small 1kw inverter for 110v uses.
Now I have a very small electric outboard (50ah maximum load) for my dinghy and have been using the lead acid from the motor on it but its not very practical (to take on and off a 27,5kg of battery to the dinghy everytime).
So I already bought a 50ah lifepo4 with 60amp BMS for it.
Anyone know Whats the cheaper way to charge my small lifepo4 in my boat?
Should I buy a DC to DC charger for it?
Is there any other cheaper way as Im in a very low budget.
I dont need it to fastcharge as I just use the dinghy like 10 minuts per day so Im thinking if theres small chargers I could buy or something like that.

Thanks in advance for any tip.

 

[cs1234]

So, I have a 32 feet monohull boat and live in it.
We have 500w of solar with MPPT for it and house bank of 315ah of lead acid and an 105ah lead acid for the motor with an alternator that can charge both banks.
I have a small 1kw inverter for 110v uses.
Now I have a very small electric outboard (50ah maximum load) for my dinghy and have been using the lead acid from the motor on it but its not very practical (to take on and off a 27,5kg of battery to the dinghy everytime).
So I already bought a 50ah lifepo4 with 60amp BMS for it.
Anyone know Whats the cheaper way to charge my small lifepo4 in my boat?
Should I buy a DC to DC charger for it?
Is there any other cheaper way as Im in a very low budget.
I dont need it to fastcharge as I just use the dinghy like 10 minuts per day so Im thinking if theres small chargers I could buy or something like that.

Thanks in advance for any tip.

Can you fit a small solar panel on the dinghy, it's cover or close to where it is stored? You could just charge the lifepo4 using a small solar panel and a small charge controller. With such little usage, a small solar panel, say 50-100 watts would probably keep it topped off.. if it's a 12v 50ah battery it only stores 600 watts and lifepo4 charges quickly and has a very low self discharge rate.

A small 12v ac/dc charger and an extension cord would probably be the cheapest easiest solution though. if you don't mind spending some money, the waterproof Victron ones are really nice. One like this. IP67 Victron 12v charger.

 

[diogocyrineu]

Yeah, I thought about the solar panels as it would be very easy... Just leave it there system. But Its gonna take too much space in my already small dinghy.
I guess the cheaper way is just to get a small 110v charger but its very ineficient.
Reprogramming my MPPT to lithium everytime would suck but more efficient lol.
Is there some way to keep 2 MPPTs plugged in the same panells? One charging the lithium and one the AGM?

 

[cs1234]

Yeah, I thought about the solar panels as it would be very easy... Just leave it there system. But Its gonna take too much space in my already small dinghy.
I guess the cheaper way is just to get a small 110v charger but its very ineficient.
Reprogramming my MPPT to lithium everytime would suck but more efficient lol.
Is there some way to keep 2 MPPTs plugged in the same panells? One charging the lithium and one the AGM?

The solar panel wouldn't need to be on the dinghy itself, if you have anywhere that small panel could sit with cabling distance of the dinghy. You would just need a small charge controller on or near the dinghy.

We aren't talking about a large number of watts here, the inefficiency of the small 110v charger probably wouldn't be that big of a loss in the grand scheme of things.

A small dc/dc charger would work, but I don't know how far you have to run from your main battery banks or nearest dc output terminal to your dinghy battery. The cabling and voltage drop could be significant for a long run.

Depending on what lifepo4 battery you got, and how closely you watched it, an AGM charge cycle run on a lifepo4 battery wouldn't be the end of the world. It's just not optimal.

No on the 2 MPPT's into the same panels. Best you could do would be to switch them back and forth, but that is something I would find highly annoying.

 

[diogocyrineu]

Yeah, thanks for the tips cs1234! I guess I will just buy a normal 110V charger! As the battery is light, I dont mind to take it inside the boat and plug in to the charger!
Its gonna be cheap and convenient! Thanks for the tips

 

[32 volt boater]

Use the solar output in place of motor of course.

There is voltage drop 0.6 but apparently the lithiums last longer at 70% charge anyway.

I bought this isolator thing, haven't messed with it yet.